પેટમાં તે પેટીમાં, ને હોઠ બહાર તે કોટ બહાર.

pēṭamāṁ tē pēṭīmāṁ, nē hōṭha bahāra tē kōṭa bahāra.

Literally: What is in the stomach is in a chest, and what is outside the lips is outside the fort.
What it means: A secret kept in one's mind remains secure, but once spoken aloud, it spreads beyond control.

Also said as

ગુજરાતી કહેવતસંગ્રહ (Gujarati Kahevat Sangrah) (1921) · read from the scan by machine — the Gujarati itself is unchecked · English is machine-made and nobody has checked it yet

Heard it differently, or know we've got the sense wrong? Tell us — that is exactly the kind of correction this needs.